1. Field of the Invention
The present invention relates to improvements in a hand-held air-driven dental vibratory instrument such as an air-driven dental scaler.
2. Description of the Prior Art
It has been customary to use powered dental vibratory instruments to carry out certain dental treatments such as scaling of teeth and reaming of root canals of teeth.
Typically, a powered dental vibratory instrument includes an elongated outer casing adapted to be held by a hand, a vibrator unit arranged within the casing to serve as a source of vibration, and a dental vibratory tool such as a scaling tip and a root canal reamer detachably connected to the vibrator unit, the dental tool being subjected to vibratory movement in response to vibration generated in the vibrator unit to thereby perform desired dental treatment such as scaling and root canal reaming.
The vibrators which are used in the powered dental vibratory instruments may be grouped into two classes according to the principle of operation; electrical vibrators wherein the vibration is generated by making use of an electric power and air-driven vibrators wherein a compressed air is used as a power source.
The electrical vibrators of the first class are disclosed, for example, in JP-A-59-25738 and JP-A-60-55941. An electrical vibrator includes an electrostrictive or piezoelectric transducer which generates vibration in response to application of an alternating voltage. The advantage of the electrical vibrators is that they are substantially free from emission of audible noise because they are operable at a supersonic frequency exceeding 20,000 Hz.
However, the problem involved in the electrical vibrators is that there is a danger that electromagnetic waves emitted from the electrostrictive or piezoelectric transducer would inadvertently cause malfunction of medical electronic and electrical devices and instruments such as a cardiac pacemaker.
In contrast, the air-driven vibrators of the other class are designed to generate vibration in response to oscillatory movement of a rotor or a vibratory element caused by a jet of compressed air supplied from a dental unit. Accordingly, dental instruments incorporating the air-driven vibrators have an advantage that they are free from the problem associated with the emission of the electromagnetic waves.
However, two fundamental problems must be overcome in designing dental instruments equipped with the air-driven vibrators.
The first problem is that a movable part such as a rotor and a vibratory element inevitably undergoes a wear as it is operated. This necessitates replacement of the rotor or vibratory element at the end of its service life. To this end, maintenance must be carried out either by dentists at individual dental clinics or by specialized mechanicians at predetermined repair centers.
The second problem is that, as normally the rotor or vibratory element of the air-driven vibrator could be oscillated only at a frequency in the subsonic or audible range, a very annoying audible sound or noise is generated which often cause a patient uneasy.
To discuss the prior art, U.S. Re. 29,687 (Sertich) discloses 30 a dental scaler incorporating an air-driven vibrator. The vibrator includes a tubular shaft resiliently supported within an outer casing and a sleeve-like rotor loosely and rotatably mounted over the shaft. Upon injecting compressed air in the tangential direction toward the inner periphery of the rotor through air nozzles formed across the wall of the shaft, the rotor is rotated about the shaft and imparts a vibration thereto. through air nozzles formed across the wall of the shaft, the rotor is rotated about the shaft and imparts a vibration thereto.
The dental scaler of Sertich enjoys the aforementioned advantage of the air-driven vibrator that it is free from the problem caused by the emission of electromagnetic waves.
Furthermore, as the rotor is mounted freely over the shaft and is axially confined by a pair of spaced O-rings fitted over the shaft, the rotor may be readily replaced whenever the rotor is worn out or damaged, by simply removing the shaft out of the outer casing and by removing the positioning O-rings. As in this manner the replacement of the rotor can be readily carried out even by the user, there is no problem of maintenance.
However, the problem of this scaler is that the air-driven vibrator incorporated therein is only able to produce a vibration having a frequency in the range of as low as 3,000-6,000 Hz. This is because vibration takes place in the so-called bending or flexural vibration mode wherein the elongated shaft is excited by the rotating rotor to oscillate by bending or flexural movement of the shaft. Consequently, this scaler cannot solve the afore-mentioned problem inherent in the air-driven vibrators that an annoying audible noise that would make patients uneasy is generated.
U.S. Pat. No. 4,453,919 (Takeshita) describes an arrangement and principle of operation of different type of air-driven vibrator which may be incorporated in a dental scaler as a source of vibration. This vibrator includes a casing provided with a disc-shaped working chamber (or rotor chamber), a disc-shaped vibratory element (or rotor) movably received in the chamber, and injection nozzles for injecting compressed air tangentially into the working chamber.
As compressed air is injected through the nozzles into the working chamber, the vibratory element is oscillated as it is rotated to strike the side walls of the chamber thereby generating a vibration. The vibration generated in the vibrator is transmitted through a shaft to a scaling tip. It is considered that the vibration transmitted through the shaft to the scaling tip is a combination of a flexural mode of vibration and an acoustic or elastic-wave mode of vibration.
U.S. Pat. No. 5,190,456 (Hasegawa) is directed to improve the dental scaler described in U.S. Pat. No. 4,453,919 (Takeshita) and proposes to increase the frequency of vibration of the vibrator as close as possible to the supersonic range in order to reduce the annoying noise inherent in the conventional air-driven vibrators.
To this end, the shaft is shorted in order to transmit to the scaling tip the acoustic or elastic mode of vibration proportionally more than the flexural mode of vibration and the shaft is supported in such a manner as to avoid the presence of a node of vibration which would give rise to the flexural mode of vibration.
According to the concept of U.S. Pat. No. 5,190,456 (Hasegawa), by reducing the size of the vibratory element (or rotor) as far as possible, the frequency of vibration can be increased to approach to the supersonic range in a manner to avoid emission of annoying noise. For example, with a vibratory element having a diameter of as small as 5 mm, the frequency of vibration will be increased up to about 15,000 Hz so that audible noise is considerably subdued.
However, increasing the frequency of vibration will, in turn, accelerate wear of the vibratory element and side walls. In addition, the more the size of the vibratory element is reduced in an attempt to increase the frequency of vibration to the degree to approach the supersonic range, the effect of wear produced on the vibratory element will be more dominant and serious and this will also shorten the service life of the element. As a result, it will be necessary to replace the vibratory element and side walls more frequently.
However, in contrast to the scaler described in U.S. RE 29,687 (Sertich) wherein the vibrator rotor may readily be replaced by anyone concerned as mentioned hereinabove, in the case of the scaler described in U.S. Pat. No. 5,190,456 (Hasegawa), it is considerably difficult for an ordinary user (e.g., a dentist) to successfully replace the vibratory element and associated wearable parts.
This is firstly because it is difficult to withdraw the vibrator unit as a whole out of the outer casing because the vibrator unit is installed deeply within the elongated outer casing. A special jig is required to drive the vibrator unit out of and into the outer casing.
The second difficulty is related to the fact that the body of the vibrator is made of a plurality of component parts including a pair of side plates defining the working chamber. Consequently, even if the vibrator unit as a whole is successfully removed from the outer casing, the user must further disassemble the vibrator body into parts in order to gain access to the vibratory element for replacement. A special tool must also be used to disassemble and re-assemble the vibrator body and such work is generally difficult to carry out for an ordinary user.
Thirdly, in the vibrator described in U.S. Pat. No. 5,190,456, it is important that the vibratory element is well matched in vibration with the side plates in order to effectively generate a high frequency vibration. It has often been experienced that mere replacement of the vibratory element or side plates is not sufficient to restore the output performance of the vibrator.
For these reasons, it has been necessary for the users of the dental scalers described in U.S. Pat. No. 5,190,456 to ship their scalers to remote repair centers or factories in order to have the worn parts or the vibrator unit as a whole replaced by skilled mechanicians. This has caused an inconvenience on the users in that the users are obliged to discontinue the use of their scalers until the scalers are repaired and returned back to the users.
Accordingly, an object of the present invention is to provide an air-driven dental vibratory instrument, including a dental scaler, which permits a user to readily replace the vibrator unit as a whole whenever replacement of a vibratory element and/or associated parts is necessary and which, therefore, is user-friendly to the effect that the user is ensured uninterrupted continued use of the instrument.
Another object of the invention is to provide an air-driven dental vibratory instrument which is so designed as to encourage the user to carry out self-maintenance and to replace a vibrator unit as a whole whenever replacement of the vibratory element and/or associated parts is necessary.
This invention provides an air-driven dental vibratory instrument, comprising,
an elongated outer casing having a longitudinally extending lodgment defined contiguous to a frontal end of the casing, said casing being split into a main body and a frontal cap which are detachably coupled with each other by means, for example, of threaded coupling,
an air-driven vibrator module or unitary assembly replaceably accommodated in said lodgment, said module having a vibratory element for generating vibration, said module having threaded coupling means for detachably coupling a vibratory tool to the frontal part of the module,
means for resiliently supporting the module in the casing,
axial positioning means for locating the vibrator module against the frontal cap,
means for supplying compressed air to the vibrator module to excite the vibratory element, and,
anti-rotation means for preventing the vibrator module from rotating relative to the casing when the vibratory tool is screwed to and unscrewed from the vibrator module. As used herein, the term xe2x80x9cfrontxe2x80x9d and xe2x80x9crearxe2x80x9d refer to the direction as seen from an user of the instrument during use.
According to the invention, the axial position of the juncture between the main body and the frontal cap is selected such that, when the main body and the frontal cap are disconnected from each other for replacement of the vibrator module, at least part of the vibrator module is exposed from the main body or frontal cap to which it is attached, to thereby permit an operator to hold the module by fingers in order to remove the module from the main body or frontal cap.
With this arrangement, whenever the user has come to believe that the power output of the air-driven vibrator incorporated in the dental instrument is lowered as a result of wearing of the vibratory element or associated parts, the user may unscrew the threaded coupling of the outer casing to disconnect the main body and the frontal cap from one another. As the main body and the frontal cap are separated, the vibrator module will remain attached to either the main body or the frontal cap, as the case may be, and the frontal or rear part of the vibrator module will be exposed from the main body or frontal cap to which it is attached. This will cause the user to recognize that the vibrator module is designed replaceable and will also visually encourage the user to replace it with a new one by him or herself.
Upon being so encouraged, the user may then remove the module from the main body or frontal cap in a simple manner, by holding the exposed part of the vibrator module by the fingers of the one hand and the main body or frontal cap by the other hand, and by merely pulling the module and the main body (or frontal cap) apart. Upon simply installing a new vibrator module to the main body or frontal cap and by screw coupling the main body and the frontal cap with each other, the dental instrument will be ready for reuse. The used vibrator module may be disposed of or sent to repair center for repair.
In this manner, the vibrator module is replaced as a whole simply by disconnecting the main body and the frontal cap from each other, by gripping a used vibrator module to remove it from the main body or frontal cap, by installing a new vibrator module thereto, and by threadingly connecting the main body and the frontal cap with each other. As all these operations may be carried out by hands without requiring a special tool or jig, replacement of the module may be done quite easily and quickly.
Accordingly, whenever the power of the vibrator is lowered as a result of wear of the vibratory element, for example, the user is able to renew the vibrator module at once, to thereby avoid any loss of time that would otherwise be necessary hitherto to ship the dental instrument for repair and to have the repaired instrument returned.
The users may be furnished with one or more spare vibrator modules which after assemblage are checked and inspected for a predetermined level of performance. Therefore, the replaced module will always develop a desired high level of vibration energy.
In one embodiment of the invention, the anti-rotation mechanism is operable to lock the vibrator module against the frontal cap. This will cause the vibrator module to remain attached to the frontal cap when the main body and the frontal cap are disconnected from each other. The axial length of the frontal cap is made smaller than, preferably roughly equal to a half of, the axial length of the vibrator module. With this arrangement, the rear half of the vibrator module will be exposed from the frontal cap as the main body and the frontal cap are disconnected, to thereby permit the operator to securely and readily grip on the module when removing the module from the frontal cap.
In this embodiment wherein the anti-rotation mechanism locks the vibrator module against the frontal cap, a torque applied to the vibratory tool as it is screwed to and unscrewed from the vibrator module will be withstood by the frontal cap. As a result, there is a risk that the frontal cap is undesirably overtightened against and loosened from the main body, as the vibratory tool is screwed to and unscrewed from the vibrator module.
To avoid such inconvenience, according to a preferred embodiment of the invention, the anti-rotation mechanism is designed to lock the vibrator module against the main body of the outer casing. With this arrangement, a torque applied to the vibratory tool to screw it to or unscrew it from the vibrator module will be withstood by the main body so that the frontal cap is exempt from the torque. This prevents the frontal cap from being inadvertently over-tightened or loosened.
In this embodiment wherein the anti-rotation mechanism locks the vibrator module against the main body, the vibrator module will remain attached to the main body when the main body and the frontal cap are disconnected from each other. The axial length of the frontal cap may be made smaller than, preferably roughly equal to a half of, the axial length of the vibrator module to ensure that the frontal half of the vibrator module is exposed from the main body to facilitate operator""s grip when removing the module from the frontal cap.
In another preferred embodiment of the invention, the axial positioning means includes a positioning sleeve extending axially within the casing and secured to the main body and the anti-rotation mechanism is operable to lock the vibrator module against the positioning sleeve to ensure that the vibrator module will remain attached to the positioning sleeve when the frontal cap is disconnected from the main body. Furthermore, the juncture between the main body and the frontal cap is located rearwardly of the frontal end of the positioning sleeve to ensure that a frontal part of the vibrator module is exposed from the positioning sleeve as the main body and the frontal cap are disconnected from each other.
As in this embodiment the juncture between the main body and the frontal cap is shifted rearwardly of the anti-rotation mechanism, the frontal cap may be rendered slim at a location at which the operator""s fingers are engaged during use of the dental instrument. This improves the operator""s grip and facilitates to precisely position the instrument during dental treatment.
Preferably, the axial length of the frontal cap is made greater than a half of the entire axial length of the outer casing and, more preferably, the frontal cap is made long enough to cover substantially the entire length of the instrument. It will be noted that it is easy to subject the frontal cap as separated from the vibrator module to autoclave sterilization and supersonic cleansing. The dental instrument may be kept more clean and hygienic by increasing the length of the cap in a manner to cover substantially the entire length of the instrument and by frequently sterilizing the frontal cap.
Preferably, the anti-rotation mechanism includes at least one notch formed on the inner periphery of the main body and at least one corresponding projection provided on the outer periphery of the vibrator module for engagement with the notch. With this arrangement, the vibrator module may readily be fitted within the lodgment provided in the frontal cap or main body. Preferably, a formation of a polygonal cross-section, more preferably hexagonal cross-section, is provided on the outer periphery of the vibrator module. This enables the user to fit the module in the frontal cap or main body only after a limited relative angular movement.
These features and advantages of the invention, as well as other features and advantages thereof, will become apparent from the following description.